Electricity + Control September 2017

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21 Electricity + Control SEPTEMBER 2017
curred deviating from the original design. After this
understanding was obtained, the team set out with
the onsite production and maintenance teams to
evaluate all the possible optimisation opportunities.
The teams debated the feasibility of each opportu-
nity and how they’d implement them to maximise
energy and water reduction.
What was found
It was discovered that the Original Equipment
Manufacturer (OEM) specified that the slurry’s
Specific Gravity (SG) should be at 1,5 at a flow-
rate of 3,0 – 3,5 m/s. However, analysis of the cur-
rent operational data showed that the slurry’s SG
was at 1,2 – 1,3 SG and at flowrates of between
3,5 – 4,0 m/s. This showed that the process was
operating differently from the original design and
indicated room for possible saving opportunities.
Throughout the team’s evaluation, it was also
found that the plant was running all the pumps
at low densities and increased speeds so as to
achieve maximum throughput (TPH) irrespective
of the actual material movement. This was done
without prioritising efficiency, resulting in the plant
consuming significantly more energy needed to
produce each ton of HMC. A factor that was also
taken into account when deciding which changes
to implement was that the quality of the HMC is
sometimes negatively affected by the metallurgi-
cal constraints of each system.
How it was solved
The approach taken by the team was incremental.
The system was first restored to the original de-
sign as there were no changes made to the intend-
ed design however the operating parameters had
changed over time. The team discovered that the
specification of the flowrates and SG had changed
– they had potentially drifted over time or changed
due to some challenge experienced in the past but
had never been reverted back after the challenge
had been overcome. After these changes, other ar-
eas of wastage were investigated and eliminated
or reduced as far as possible.
The SG was restored to the original specifica-
tion of 1,5 by first making sure that the feed of
the material to the buffer was sufficient. The solids
<<Author>>
Mbongeni
Ndlangamandla
is Project Engineer
at Ensight Energy
Solutions.
+27 (0) 83 607 5264
s
in the bin needed to be maintained at a specific
level to ensure a sufficient buffer for downstream
processing. To address the flowrates which were
higher than specified, the possibility of slowing
down the pump was investigated. Through the
use of a Variable Speed Drive (VSD) the flowrates
could be managed effectively. Energy consump-
tion of the pumps would be significantly reduced
as an added bonus.
The pumps were slowed down to reduce the
flowrate or stopped when not required to run (no
feed). When slowing down the pumps the critical
Carrying Velocity (CV) of the mineral sand need-
ed to be considered as going below the CV can
cause settling and lead to blockages. In order to
achieve this and as a safety measure, when the
feed was off or there was no sand for 20 minutes
the pumps reverted to the critical carrying velocity
to ensure maximum energy saving. If after 20 min-
utes no sand was processed in the plant, some
equipment was even switched off to reduce the
energy consumption further.
An important factor for the team throughout the
evaluation and implementation process was to en-
sure that the changes made did not affect the mines
production output at all. The company’s primary fo-
cus was to implement management of change pro-
jects before capital projects were considered.
Conclusion
This project has achieved savings of 88 395 MWh
of energy which equates to R56 M and water sav-
ings of 3 646 ML from inception to date (May 2014
– May 2017). Furthermore, throughput increased
by 20% and maintenance breakdowns reduced
by 50%. The company remains on site at this
particular mine and, to date, has achieved over
R261 M worth of savings for the company
through its energy saving and optimisation pro-
jects − translating into 164 000 tonnes of green-
house gas emissions saved.
This project has
resulted in R261 M
savings for the
company through
its energy saving
and optimisation
projects −
translating into
164 000 tonnes of
greenhouse gas
emissions saved.